Not applicable
1. Field of the Invention
The present invention relates to nanocomposites. More particularly, the present invention relates to a method of producing nanocomposites using reverse micelles and to the nanocomposites so formed.
2. General Background of the Invention
Present technology is reaching the limit of usefulness due to the small sizes required. As a result, new synthetic methods are being used to synthesize materials. It has been shown that granular Fe/Au and Co/Au alloys synthesized using traditional ball milling methods have an improved GMR effect over thin-films. Studies by others have elucidated the role of surface spins in the origins of GMR while uniformity has also been demonstrated as key. Present technology is limited due to scalability and versatility.
In ferrofluid applications and biochemical applications, the current technology is limited due to magnetic field required and the size of the particles involved.
The following U.S. patents are incorporated herein by reference:
U.S. Pat. Nos. 5,879,715; 5,889,091.
The present inventors have made a nanocomposite comprising a diamagnetic core of a material from the group consisting of gold, silver, copper, and platinum; a thin layer of magnetic material from the group consisting of iron and cobalt and alloys (including platinum alloys) containing iron and/or cobalt, formed on the diamagnetic core; a passivating layer of diamagnetic material from the group consisting of gold, silver, platinum, and copper, and alloys containing these materials, formed on the layer of magnetic material. In a preferred example, the diamagnetic core is made of gold, the magnetic material is made of iron, and the passivating layer is made of gold.
The present invention comprises a method of producing nanocomposites and the nanocomposites so produced.
Reverse micelles have been proven useful as nano-reactors for the growth of metal colloids. The present inventors have adapted the process to sequentially grow first a magnetic core material (either Iron or Cobalt) and then the surface is coated with a diamagnetic coating. This techniques has several advantages over current methods:
Reverse micelles technique forms more uniform size and shaped particles, which is essential in current semiconductor and computer applications.
It is easily scalable, so the reaction can be modified for the generation of large quantities of nanoparticles.
The high uniformity in the particles allows for improved magnetic and electronic properties.
The presence of the diamagnetic coating passivates the magnetic core thus protecting the magnetic properties without having a pronounced effect on the magnetic properties.
The presence of the diamagnetic coating allows for a surface that can be derivatized to allow for greater versatility while not reducing the magnetic properties.
This process can be modified to form stable nanoparticles of iron or cobalt useful in a variety of applications ranging from ferrofluids to granular GMR materials.
Possible areas in which this invention can be used commercially are in the semiconductor industry for novel inductor materials, as well as in the computer industry where it potentially could be used as an innovative storage media. Material synthesized in this fashion could also be used as giant magnetoresistance (GMR) sensors, which have application in a wide variety of applications from automobiles to computers.
The stability of the surfactant coated metal colloids allows for the creation of ferrofluids, which are usable applications from petrochemical industry to consumer electronics. The biocompatability of the granular materials also allows for potential uses as directed drug delivery and targeted sensing for in vivo applications.
In ferrofluid applications and biochemical applications, the current technology is limited due to magnetic field required and the size of the particles involved. By using nanocomposite materials synthesized in this fashion, the enhanced magnetic properties of metals can be used while remaining chemically inert.
The present invention also comprises an innovative giant magnetoresistance (GMR) material.
The present inventors have modified a reverse micelle synthesis technique to generate an innovative giant magnetoresistance material. Using cetyltrimethylammonium bromide, n-butanol, octane and aqueous reactants, the present inventors have been able to synthesize an inventive new nanocomposite. The composite has a gold core onto which a thin layer of iron is grown, which is then passivated with gold. These composites, which the present inventors have dubbed xe2x80x9cnano-onionsxe2x80x9d, have several advantages over traditional GMR materials. 1) The materials were synthesized using the reverse micelle technique, which has numerous advantages over standard methods. 2) The material has a drastically increased surface area and thus a larger GMR response is measured compared to other materials of similar composition. 3) The presence of gold allows for greater functionality and protection of the magnetic component. 4) This is the first material of its type that has been synthesized using the reverse micelle technique.
Present technology is reaching the limit of usefulness due to the small sizes required. As a result, new synthetic methods are being used to synthesize materials. It has been shown that granular Fe/Au and Co/Au alloys synthesized using traditional ball milling methods have an improved GMR effect over thin-films. Studies by others have elucidated the role of surface spins in the origins of GMR while uniformity has also been demonstrated as key. Since the method of the present invention generates materials that have a significantly higher degree of uniformity as well as a dramatically larger percentage of surface spins, they display a larger GMR effect over materials with similar compositions. Present technology is limited due to scalability and versatility.
By utilizing the sequential synthesis afforded reverse micelles, nanocomposite materials can be synthesized which have a diamagnetic core surrounded by a thin shell of ferromagnetic material passivated with a second shell of a diamagnet. Using gold as the diamagnetic material and iron as the ferromagnetic material, nanocomposites can be synthesized where there is a thin layer of the magnetic material, which is passivated and protected from oxidation. In this case, all of the spins of the magnetic layer lie within the surface of the particle.
Magnetic properties were measured for nanophase particles using SQUID magnetometry. The particles, which consist of a 6 nm core of gold, coated with a 1 nm thick iron layer and passivated with an outer shell of gold, are superparamagnetic with a blocking temperature of 45 K and coercivity at 10 K of 400 Oe. These results are similar to magnetic properties of 8 nm iron particles coated with gold, where blocking temperature is 50 K and coercivity is 400 Oe. This suggests that in nanoparticles the spins that define the outer surface are responsible for the magnetic properties.